Cellular communication systems have entered our daily life since the early nineties. Recent years have seen tremendous improvements in the field of cellular communication which has led to an unprecedented wireless revolution. The main reason for these improvements is the achievable high integration level of Complementary Metal Oxide Semiconductors (CMOS), hereinafter referred to as CMOS. This gave rise to the integration of a huge number of digital functionalities into a single chip which resulted in the powerful cellular communication networks of today. Another important reason for the successful development of cellular communication is the low cost of the user equipment due to the low cost of CMOS transistors.
There are multiple services like telephony, internet, video conference, email, etc being incorporated into the cellular communication systems, nowadays, which demands a higher level of integration in order to keep the cost of the user equipment reasonable and at the same time provide increased battery life time with low power consumption. Equipment of cellular communication networks requires a power amplifier to amplify the radio signal before it is transmitted through the antenna. Therefore, the radio signal is amplified by a power amplifier before it is transmitted through the antenna. Hence the amplification of the radio signal should be done to a desired output power level without consuming too much power in order to save battery lifetime. In other words, besides the required output power, the power amplifier should have sufficient linearity, high efficiency and gain.
In order to achieve the requirements stated above, current commercially viable power amplifiers must be realized in costly compound semiconductor processes such as GaAs. On the other hand, the active field of CMOS power amplifier design needs much effort directed towards the creation of the needed output power using power combiners. In most of the time this is achieved by using transformers on the drain side of the output transistor. However, the low voltage handling capability of normal CMOS transistors forces the usage of very large output impedance transformation ratios, which in turn end up encountering significant losses in the power combining circuit. Therefore, the performance of the power amplifier in terms of maximum output power, power added efficiency and ruggedness is therefore compromised relative to a GaAs based power amplifier.
In view of the foregoing, there is a need for a driver circuit to drive the output power of a power amplifier such that it minimizes the cost incurred due to costly compound semiconductor materials.